Google Chrome has a handy feature where I can click a download link and drag it into a Windows Explorer window, and then drop. After dropping, Chrome then downloads the file and it appears where I dropped it.

I would like to be able to drop from Google Chrome into my application, but it seems it isn't so simple. I have a DataGridView called gridFiles, and the following code:

Private Sub gridFiles_DragDrop(ByVal sender As Object, ByVal e As System.Windows.Forms.DragEventArgs) Handles gridFiles.DragDrop
If e.Data.GetDataPresent(DataFormats.FileDrop) Then
Dim DroppedFiles() As String = e.Data.GetData(DataFormats.FileDrop)
If Not DroppedFiles Is Nothing Then
For Each file As String In DroppedFiles
MsgBox(file)
Next
End If
End If
End Sub
Private Sub gridFiles_DragEnter(ByVal sender As Object, ByVal e As System.Windows.Forms.DragEventArgs) Handles gridFiles.DragEnter
If e.Data.GetDataPresent(DataFormats.FileDrop) Then
e.Effect = DragDropEffects.All
End If
End Sub

When I drop files onto it from Windows Explorer, all works fine and I get a message box for each file that was dropped. However, when I drop from Chrome, nothing happens. The reason for this is that DroppedFiles is equal to Nothing. It seems that e.Data.GetData isn't returning anything. I have checked the formats with e.Data.GetFormats() and it returns FileDrop, FileName, FileNameW as expected with any file drop.

What I am quite sure is happening is that Chrome says it has some files so that the DragEnter functions, but since it hasn't downloaded the file yet, DragDrop cannot be done, so Chrome returns no files. I suspect that in a Windows Explorer context, Chrome somehow gets that window's path and copies the file there itself later.

So my question is...

How can I fool Google Chrome into dropping into my application? I see this working by somehow giving Chrome a temporary folder where it thinks it has dropped the file, and my application would monitor that folder for new files and pull them in once they are downloaded. I just need to find a way for Chrome to "know" that folder.

Alternatively, if I could get the URL of what was dropped, that would be just fine as well. I could then download the file with my program.

Any and all advice is much appreciated. Thanks.

EDIT: So it seems that with regular URLs, I do get the proper dragged-in UniformResourceLocator format. The behavior I am seeing occurs with the download links in Gmail. It probably happens elsewhere, but I am not sure. When a gmail attachment is dragged from Gmail into my application, I get a FileDrop.

Doing some more digging, it seems that Gmail is using the download_url attribute of the anchor tag. I have never heard of this before. Perhaps this is just an extra property they have added?

In any case, since my application will primarily be used with e-mail attachments, I need a way for the phantom FileDrop to work, as stated above. I am unable to use Spy++. It doesn't seem to show any messages when drops occur. (I welcome any advice on that problem as well.)

on some downloads (not peRmalink urls) your app won't have the necesary session state (cookies) to have access to the desired file.
–
Luis SiquotMay 27 '11 at 20:34

@Luis, I understand what you are saying now. Yes, having Chrome do the downloading is my first preference, but downloading the file later (even if that means only handling URLs that don't require login/session) is acceptable for my application as well.
–
BradMay 27 '11 at 20:49

1

Instead of relying on DataFormats.FileDrop you might want to check which values are returned by e.Data.GetFormats(). Doing some quick tests it looks like the format "UniformResourceLocator" (or even "Text") makes e.Data.Get(...) return a MemoryStream that contains the URL to the dragged link in plain text. Maybe this is something to investigate further.
–
jCoderMay 27 '11 at 22:55

3 Answers
3

I've pulled kilometers of hair out of my head myself regarding weird drag-drop behaviour. Spy++ as mentioned by sixlettervariables might be a good idea. Another would be to take a look at the discussion from one of my Q/As here at SO:

Any advice on getting Spy++ working? I can't get it to show any drag/drop messages.
–
BradMay 31 '11 at 15:20

Sorry, I just know I had similar issues and found browser-stuff to be very restricted. If you figure this out, I'll be implementing a version of it in one of my own apps :)
–
PederyJun 1 '11 at 3:12

unfortunately, it doesn't look like I am going to figure this one out, heh. Only 2 days left on the +100 bounty, and I don't even know where to begin to track this one down. The only idea I can think of is to actually put some explorer component on my form, but that is less than ideal. I'm not even sure it would work.
–
BradJun 1 '11 at 13:50

I edited my answer. Maybe the solution in the link works for you.
–
PederyJun 3 '11 at 5:35

Have you considered using Spy++ to see what messages are sent from Chrome to Windows Explorer? Spy++ has message logging which has helped me in the past with strange behavior. You can enable logging of WM_DROPFILES, etc.

Yes, I used Spy++ but didn't see any messages, until after the drop, and then it was just MOUSEMOVE and what not. (In fact, I was just posting a separate question regarding that!) I will go back and see if there is a filter or something enabled.
–
BradMay 27 '11 at 19:20

I can't get Spy++64/32 to generate the WM_DROPFILES message either, but I'm on a 64bit machine which may just complicate things.
–
user7116May 27 '11 at 19:30

Anyway, in case Chrome does the drag & drop with virtual sources, that is, it downloads the file and generates the content on drag & drop completion, you have to implement shell interface IDropTarget. I get the feeling the file contents might be transferred via IStream which is not supported by .NET Drag&Drop.